1. Field of the Invention
The present invention relates to a rubber composition for a tire tread. More specifically, it relates to a rubber composition for a tire tread, especially suitable for use as a large sized tire such as a truck or bus, having a remarkably improved balance of heat generation resistance, processability and abrasion resistance.
2. Description of the Related Art
In rubber compositions for large sized tires such as those for trucks and buses, rubber composition for tire treads containing carbon blacks having a small particle size, such as ISAF-SAF class carbon blacks to improve the abrasion resistance.
However, these rubber compositions containing such carbon blacks have problems that the abrasion resistance and the processability become worse. To solve these problems, many proposals containing carbon blacks such as those having small particle sizes, improved surface activities, aggregate forms, etc. have been made (see, e.g., JP-A-64-74242, JP-A-63-264647, JP-A-3-121165, JP-A-2-77445, JP-A-2-140244, JP-A-2-286727).
However, when the above-proposed carbon blacks are compounded into rubber compositions, the abrasion resistance, the heat generation resistance and the processability are not sufficiently improved.
Accordingly, the present inventors tried to optimize the below-mentioned characteristics of carbon blacks, mainly to improve the abrasion resistance in view of the heat generation resistance and the processability. As a result, it was found that the preferable carbon blacks can be obtained when carbon blacks have a particle size equal to those of general SAF class, a sharp .DELTA.Dst and a high Tint for the abrasion resistance, when the surface activities, especially toluene discoloration (T%), are optimized for the heat generation resistance, and when carbon blacks are low structured and T% and N.sub.2 SA/IA ratio are optimized.